Integrative Activity and the Role of Cortical Neurons
Nerve cells of the cerebral cortex directly participate in regulating complex behavioral acts. This involvement can occur throughout the entire action or during specific, strictly defined stages.
A fundamental concept in this topic is neuronal integrative activity. It represents the unique capacity of a cell to receive and process diverse arrays of information before generating its own excitation.
The significance of this activity is that each individual neuron contributes its unique input to the overall global excitation system of the brain. This is how a cohesive, adaptive behavioral act is formed. The impulse activity recorded in cortical neurons reflects two major aspects:
- Spatiotemporal and probabilistic parameters of the external environment.
- The organism's attitude toward this environment, including attempts at its active, goal-directed transformation.
Dynamics of Behavioral Act Formation
Behavior formation during learning progresses through several consistent stages, each characterized by a distinct set of afferent (incoming) signals.
- Baseline level (in an unconditioned/naive animal). The initial foundation consists of motivational excitation (internal drive) and situational afferentation (signals from various sensory organs regarding environmental conditions).
- The learning process. As the skill is acquired, feedback afferentation (reverse afferentation) is necessarily integrated into the baseline structure. This information flow informs the nervous system about movement parameters, allowing for real-time corrections.
- Achievement of the result. Successful completion of the action leads to reinforcement. Physiologically, this stage is always accompanied by a pronounced emotional evaluation and predictably results in sharp fluctuations in the initial level of motivational excitation (typically decreasing it upon satisfaction of the need).
Experimental Model and Timeline
To study brain activity, behavior is broken down into clear temporal stages. A classic example is food-acquisition behavior in a cat inside an experimental chamber:
- Stage I: The animal presses a special pedal.
- Stage II: The moment milk appears in the feeder (direct reinforcement).
- Stage III: The animal begins licking the milk.
During the experiment, researchers record single-unit discharge activity. This can be presented as a single activity trace over the course of one behavioral act (Type A) or as cumulative histograms. In the latter case, neuronal activity is averaged across 10 repetitions of the act (Types B, C, D), revealing reliable patterns.
Neurochemical Basis: Pharmacological Analysis
Neuronal recruitment into a behavioral act occurs exclusively via chemical pathways. This is demonstrated by microiontophoresis, a technique that allows precise application of neurotransmitters directly to a cell while measuring changes in its activity pattern.
Studies focused on a neuron that, under normal conditions (control), exhibited a characteristic increase in impulse activity strictly beginning at the moment of the pedal press.
- Effect of acetylcholine: Microiontophoretic application of this neurotransmitter eliminated the discharge at the moment of the pedal press (Stage I) and significantly decreased impulse activity during reinforcement itself (Stages II and III).
- Effect of norepinephrine: Administration of norepinephrine caused a generalized, rather than selective, decrease in the baseline activity of the nerve cell. This inhibitory effect was consistently observed across all stages of food-acquisition behavior without exception (both before and after pressing the pedal, as well as during eating).